A comparison of maximum likelihood sequence detection and nonlinear decision feedback equalization on the digital magnetic recording channel

The magnetic recording channel at high-density exhibits significant nonlinear intersymbol interference, which degrades the performance of linear equalization techniques. The RAM-DFE has been proposed as a solution to the problem, in which a digital RAM is used in the feedback path of a decision feedback equalizer (DFE). It is capable of canceling the nonlinear post-cursor intersymbol interference. Maximum-likelihood sequence detection (MLSD) offers the best performance attainable on these binary-input finite-memory channels; however, the complexity grows exponentially with the memory length. It was found that about 6 dB of detection signal-to-noise ratio is lost to nonlinear effects, and the RAM-DFE can retrieve about 1.5 dB. A gap of about 6 dB remains between the RAM-DFE performance and the MLSD bound, which suggests the possibility of improved receivers for nonlinear channels